1. Field of the Invention
The invention relates to an electrical cable for supplying power from a power source to a consumer unit, said cable comprising at least one interruption region in which a component for interrupting the power flow is arranged.
2. Description of Related Art
An electrical cable of this type is known from the German patent specification 40 06 866. This cable provides a conventional fuse element in the shape of a safety fuse in the interruption region, said safety fuse being surrounded by an electrically insulating housing. Together with two contact bodies with which the two ends of a fusible wire are conductively connected, there are two plug and socket connections for a plug connection each. Consequently the housing is configured as a sleeve for removable accommodation of a fuse cartridge. Such types of fuses are commonly used in motor vehicle construction.
To switch the current flow in current-carrying cables, in general, semiconductor components such as e.g. transistors, thyristors and similar are used, with the ends of the electrical cables being connected to said components. Due to the voltage drop present at a semiconductor switch even in the switched-through state, dissipation power results, which gives rise to dissipation heat. For this reason, in the case of high-current applications, the semiconductor component must be provided with a cooling device so as to carry away the dissipation heat. Such a semiconductor switch is known from DE-AS 1039645.
Power transistors are also known from the state of the art.
Usually, contacting in power transistors is by way of bond wires. The semiconductor chip comprises metallic surfaces to which a thin metallic bond wire is welded. This process of bonding causes problems above all in the case of very thin chips, for example chips with a thickness of less than 150 xcexcm, so that there is a danger of the semiconductor being destroyed by thermomechanical tension.
It is thus the object of the invention to improve an electrical cable of the type mentioned in the introduction, to the extent that as little dissipation heat as possible arises.
This object is met in that the component is a controllable semiconductor component, in particular a semiconductor chip whose effective contact surfaces in the interruption region, are directly connected by the effect of pressure to the faces of the connection sections of the cable.
According to the solution provided by the invention, as a result of direct surface contact between the connection surfaces of the cable sections and the effective cross-sectional surface of the semiconductor component, the junction resistance is almost eliminated and accordingly, no dissipation heat arises in that location. Furthermore, the integration of the semiconductor component in the interruption region of the electrical cable makes possible a compact design characterized by particularly high stability due to the effect of the mutual pressure between the end sections of the cable and the semiconductor component.
The semiconductor component can for example be a power field effect transistor whose cathode is connected to one end of the cable, and whose anode is connected to the other cable. Furthermore, the semiconductor component can comprise a control electrode, for example a gate connection or a base connection, by way of which the semiconductor switch can be driven, and controlled or blocked more or less conductively.
According to a first preferred embodiment of the invention, the pressure exerted in the area of the semiconductor element can be generated, in that a housing is provided which encloses the interruption region of which there is at least one; said housing comprising pressure means, in particular pressure springs, for exerting pressure on the connection sections of the cable against the effective contact surfaces of the semiconductor element. The metallic housing itself can be configured as a pressure means, for example if it functions as a pressure spring. To produce such a component, before or during encasing of the housing, the connection areas which form the high-current contacts of the semiconductor element, which areas can in particular also be formed by compressed conductor ends, are pressed at a pressure exceeding 100 N/mm2 onto the contact surfaces of the semiconductor chip. After encasing the housing, this pressure is held by the metallic housing.
In a further preferred embodiment, the metallic housing and/or the surfaces of the connection sections of the cable are coated so as to be at least partly electrically insulating, or the electrical insulation is formed by an insulating washer between the metallic housing and the high-current contact.
In an alternative to the housing enclosing the interruption region, the interruption region can also be surrounded by a plastic encapsulation, within which he exists pressure, particularly, thermally generated and/or reinforced pressure. The encapsulation can be formed by spraying, such that the pressure applied during the spraying process after cooling the sprayed material is frozen, and as a result of natural shrinkage during the cooling phase of the plastic, may be reinforced. Instead of plastic, a suitable ceramic material or a fiber-reinforced material can be used.
As an alternative, encapsulation can also take place by pouring-in the high-current contacts such that the pressure exerted before and during the hardening process is frozen after hardening of the material and is further reinforced by the natural shrinkage during hardening.
In a further alternative, pressure can be exerted by means of screwing down the high-current contacts such that a previously applied pressure in the area of the contact surfaces remains or is further reinforced by thermal influences.
An important aspect of the invention deals with the design of the control electrode of the semiconductor element (e.g. gate connection) of a power field effect transistor whose effective contact surface is connected to an electrical drive unit arranged in the interruption region.
According to a first variant, the means of contact can be a spring contact pin which in particular is arranged so as to be concentric with the ends of the cable connectors. This variant is particularly suitable where the high-current contacts of the main electrodes are formed by pressure contacts. Such main electrodes are formed by the drain/source connections in the case of field effect transistors; and by the collector/emitter connections in the case of power transformers.
As an alternative to the above, the means of contact of the control electrode is a passive radio receiver. It is arranged directly on the chip, in close proximity to the control electrode. In its simplest embodiment, the radio receiver comprises an aerial structure, a diode, and a coil which for example are etched in MOS technology. In a further embodiment, the receiver designed in this way may comprise several oscillating circuits with different resonance frequencies, for example to allow improved addressing of the receiver.
As an alternative to the above, the means of contact of the control electrode is provided by a sound pickup which for example works in the ultrasonic or hypersonic range. To this effect, a sound pickup is installed directly on the chip, in close proximity to the control electrode. In its simplest embodiment, said sound pickup is an aerial structure etched onto piezoelectric material. As an alternative to this, the receiver may comprise structures configured in the shape of an interdigital filter, thus making digital coding possible.
In a further alternative, the contact means is an optoelectronic receiver which is also arranged directly on the chip in close proximity to the control electrode. Said receiver comprises an optoelectronic semiconductor structure at whose outlet the gate control voltage is made available.
The spatial arrangement of the control electrode in relation to the remaining connections of the power semiconductor element is preferably selected such that it is centred. The edge arrangement of the control electrode is preferably circular or polygonal so that the highest possible current densities can be achieved.